Field of the Invention
The present invention relates to a preferable overhead valve actuation mechanism used for an engine mounted on a vehicle, such as a motorcycle.
Description of the Related Art
Conventionally, for example as described in Patent Document 1, a valve gear includes a rocker shaft and a rocker arm. The rocker shaft has an axis line parallel to a camshaft inside a cylinder head. The rocker shaft is disposed at a position projecting from a coupling face as viewed from an axial direction of the camshaft and supported by the cylinder head. The rocker arm is turnably borne by the rocker shaft so as to swing following a rotation of an air exhaust side valve motion cam disposed in the camshaft.    Patent Document 1: Japanese Laid-open Patent Publication No. 2009-243401
In a conventional valve gear, a camshaft is arranged in a side of an intake valve inside a cylinder head. Therefore, the cylinder head that holds a valve drive system in this air intake side becomes large in size to narrow a peripheral space of the cylinder head. Due to such positional relationship with the camshaft, it is difficult to ensure a close arrangement of a throttle body to which the cylinder head is coupled. Also, an intake port of the cylinder head needs to be formed long. Thus, a problem, such as a difficult layout of auxiliary machine components in the air intake side, is caused.